Background/Aims: Sequential antiviral therapy for chronic hepatitis B may lead to the selection of multidrug-resistant mutation. This study was carried out to assess the efficacy of entecavir in patients that have experienced adefovir monotherapy failure after the development of lamivudine resistance. Methodology: Fifty-three patients with confirmed genotypic lamivudine-resistant chronic hepatitis B were treated with entecavir. Thirty patients were switched to entecavir directly (LAM-ETV group), whereas the remaining 23 were adefovir-refractory patients who were switched to entecavir (LAM-ADV-ETV group). These 23 patients included 9 patients with inadequate response (ADV-I subgroup) and 14 that exhibited adefovir resistance (ADV-R subgroup). Results: Significantly greater reductions in HBV DNA levels were observed after 24, 48 and 72 weeks of entecavir therapy in the LAM-ETV group than in the LAM-ADV-ETV group, respectively. However, between these two groups at 48 and 72 weeks, no significant differences were observed in cumulative proportions of virological response or breakthrough, respectively. Furthermore, efficacy of entecavir was not significantly different in the ADV-I and ADV-R subgroups. Four patients in the LAM-ETV group and six patients in the LAM-ADV-ETV group developed genotypic resistance to entecavir. Conclusions: Entecavir therapy is less effective in adefovir-refractory patients with prior lamivudine resistance than in lamivudine-resistant patients.